Coaxial conductor interconnection wiring board

ABSTRACT

A coaxial conductor interconnection wiring board includes at least one coaxial conductor and at least one conductive hole having an inner wall covered with a metal film connected to a central signal conductor of the coaxial conductor. The conductive shield of the coaxial conductor is connected to the ground layer by connection metal layers. A conductor insulating layer surrounds the metallized conductor hole and the connection metal layers surround a part of the additional conductor insulating layer. Thus, the conductive hole, insulating layer, and connection metal layers function as a coaxial conductor.

BACKGROUND OF THE INVENTION

This invention relates to a coaxial conductor interconnection wiringboard and a process for producing the same.

With the development of electronic devices, wiring boards having a veryhigh wiring density have been required. As such wiring boards having avery high wiring density, there are known wiring boards using wires as anecessary wiring pattern (hereinafter referred to as "multi-wire wiringboard", e.g. Japanese Patent Examined Publication No. 45-21434) andmulti-layer printed wiring boards. In highly densified wiring boards,the crosstalk noise among neighboring wires or signal conductor linesbecomes an important problem. In order to solve such a problem, thereare proposed various processes for shielding wiring boards, for example,a process for making signal conductor lines and a grounding pattern bybuild-up method (Japanese Patent Examined Publication No. 58-54520), aprocess for using an electroconductive coating film as a shield(Japanese Patent Unexamines Publication No. 51-71961), a process forproviding a conductive shield surrounding insulated wire conductors byplating method (U.S. Pat. No. 4,646,436), etc. But these processes areinsufficient for solving the problem of crosstalk noise.

On the other hand, in order to improve these shielding processes, thereare proposed processes for using a so-called coaxial conductor coveredwith a conductive shield on an outer insulating layer surrounding asignal conductor (U.S. Pat. Nos. 4,679,321 and 4,743,710). When suchcoaxial conductors are used, connections of a central signal conductorand a conductive shield of the coaxial conductor with other conductorsbecome a problem. According to U.S. Pat. No. 4,743,710, there areproposed two processes. According to a first process (shown in FIGS. 1Ato 1E of said U.S. Patent), it is necessary to remove anelectroconductive substance, and a conductive shield and insulation ofthe coaxial conductor using a focussed laser at a portion to beconnected, while retaining only a central signal conductor. But when thelaser energy is made small so as not to remove the central signalconductor of coaxial conductor, removal of the portions to be removedcannot be carried out completely. In contrast, when the laser energy ismade large so as to remove the portions to be removed completely, thecentral signal conductor is also vaporized or damaged. Thus, it isdifficult to determine conditions satisfying both requirements and tomaintain such a laser energy constantly. Further, according to thedescription at lines 58 to 67 on column 3 of said U.S. Patent, thecentral signal conductor reflects the CO₂ laser energy and other organicmaterials can be removed. But since the organic ground layer (here, anelectroconductive paste is imaged) has high electroconductivity, theshielding effect becomes small. According to a second process (shown inFIGS. 2A to 2F of said U.S. Patent), it is necessary to etch backselectively the conductive shield of coaxial conductor exposed to aninner wall of hole. In order to attain such a selective etch back, it isnecessary to use different materials for the conductive shield and thecentral signal conductor of the coaxial conductor. Further, this meansthat it is difficult to insulate the inner portion of hole including theselectively etched back portion and a surface of the ground layer. Whendifferent materials are used for the conductive shield and the centralsignal conductor of coaxial conductor, the decay of signal of centralsignal conductor becomes larger in the case of using a poorelectroconductive material for the central signal conductor of coaxialconductor, while the shielding effect becomes smaller in the reversecase. Further, when the conductive shield of coaxial conductor isselectively etched back, very small vacant spaces are formed in theetched back portions. It is difficult to fill such vacant spaces with aresin solution, and even if filled with the resin solution, generationof undesirable voids is inevitable due to vaporization of a solventcontained in the resin solution.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a coaxial conductorinterconnection wiring board without crosstalk noise, excellent inshielding effect and suitable for high speed signal management, and aprocess for producing the same.

The present invention provides a coaxial conductor interconnectionwiring board comprising a circuit substrate (2') having a ground layer(1), or an insulating substrate (2) formed on a ground layer (1), anadhesive insulating layer (3) formed on said circuit substrate (2') orsaid insulating substrate (2), at least one coaxial conductor (4) fixedon the surface of said adhesive insulating layer (3) with a desiredshape, an insulating layer (11) covering said coaxial conductor (4), andat least one conductive hole (8), the inner wall of which is coveredwith a metal layer connected to a center signal conductor (7) of saidcoaxial conductor (4), connection of a conductive shield (5) of saidcoaxial conductor (4) to said ground layer (1) being obtained by atleast one inner wall metallized conductive hole (6) or connection metallayers (6'), and connection of said center signal conductor (7) to saidinner wall metallized conductive hole (8) being obtained by using saidcoaxial conductor from which a part of conductive shield (5) has beenselectively removed.

The present invention also provide a process for producing the coaxialconductor interconnection wiring board mentioned above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partly cross-sectional and perspective view of one exampleof the wiring board of the present invention.

FIG. 2 is a partly cross-sectional and perspective view of anotherexample of the wiring board of the present invention.

FIGS. 3 to 17 are cross-sectional and perspective views andcross-sectional views explaining the processes for producing the wiringboard of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The coaxial conductor interconnection wiring board of the presentinvention referring to FIGS. 1 and 2, comprises a circuit substrate (2')having a ground layer (1), or an insulating substrate (2) formed on aground layer (1), an adhesive insulating layer (3) formed on saidcircuit substrate (2') or said insulating substrate (2), at least onecoaxial conductor (4) fixed on the surface of said adhesive insulatinglayer (3) with a desired shape, an insulating layer (11) covering saidcoaxial conductor (4), and at least one conductive hole (8), the innerwall of which is covered with a metal film connected to a center signalconductor (7) of said coaxial conductor (4), connection of a conductiveshield (5) of said coaxial conductor (4) to said ground layer (1) beingobtained by at least one inner wall metallized conductive hole (6) orconnection metal layers (6'), and connection of said center signalconductor (7) to said inner wall metallized conductive hole (8) beingobtained by using said coaxial conductor from which a part of conductiveshield (5) has been selectively removed.

One example of the wiring board of the present invention has thestructure as shown in FIG. 1 (hereinafter referred to as "inner wallmetallized conductive hole containing type"). Another example of thewiring board of the present invention has the structure as shown in FIG.2 (hereinafter referred to as "connection metal layer built-in type").

The inner wall metallized conductive hole containing type wiring boardhas a structure as shown in FIG. 1 comprising a circuit substrate (2')having a ground layer (1), an adhesive insulating layer (3) formed onthe circuit substrate (2'), at least one coaxial conductor (4) with adesired shape fixed on the surface of the adhesive insulating layer (3),at least one inner wall metallized conductive hole (6) connected to aconductive shield (5) of the coaxial conductor and the ground layer (1),and at least one inner wall metallized conductive hole (8) connected toa central signal conductor (7) of the coaxial conductor, connection ofthe central signal conductor (7) to the inner wall metallized conductivehole (8) being obtained by using the coaxial conductor from which a partof conductive shield (5) has been selectively removed.

Such a wiring board can be produced as follows.

As shown in FIG. 3, on a surface of circuit substrate (2') having aground layer (1), an adhesive insulating layer (3) is formed and aplurality of coaxial conductors (4) are placed on the adhesiveinsulating layer in a desired shape, followed by fixing (Step A).

As the substrate (2') for forming the ground layer, there can be used acopper-clad laminate commercially available. It is also preferably useda polyimide film on which surfaces copper foils are formed and which isgood in laser processability, a metal foil coated with a thermosettingor photocurable resin mixed with an organic filler, particulateinorganic filler, short fibrous inorganic filler, or the like, acopper-clad laminate obtained by using a resin reinforced with clothmade from an organic material such as aramide fibers (aromatic polyamidefibers), etc.

As the adhesive insulating layer (3), there can be used resincompositions which can adhere coaxial conductors thereto, for example,containing natural rubber or synthetic rubber and an epoxy resin asmajor components.

As the coaxial conductor (4), there can be used commercially availableones. In order to obtain higher density and to improve wiringworkability, it is preferable to use a coaxial conductor as shown inFIG. 8 wherein numeral 5 denotes a conductive shield, numeral 7 denotesa central signal conductor, numeral 9 denotes a conductor insulatinglayer, and numeral 13 denotes a conductor adhesive layer excellent inadhesive strength with the adhesive insulating layer (3).

As the conductor adhesive layer (13), there can be used polyvinylbutyral/epoxy resin, nylon/phenol resin, and the like.

As the central signal conductor (7) of coaxial conductor (4), there canbe used a single wire or twisted ones. The central signal conductor canhave a diameter of 30 to 80 μm and can be made of copper, a copperalloy, aluminum, an aluminum alloy, or can be a copper-clad music wire,or wires made of the materials mentioned above and plated with gold,silver, or tin.

The conductive shield (5) of coaxial conductor can be formed by platingcopper or a copper alloy, or by winding a wire of 20 to 30 μm indiameter made of copper, a copper alloy, aluminum, or an aluminum alloyor a copper-clad music wire on the surface of the conductor insulatinglayer (9). Further, the conductive shield (5) can be formed by winding astrip of copper or a copper alloy, or a strip of copper- or copperalloy-clad foil.

As the conductor insulating layer (9), there can be used a polyimide, apolyamideimide, a fluorine resin, a methylpentene resin, etc.

As shown in FIG. 4, an insulating layer (11) is formed so as to fix thecoaxial conductors (4) (step B).

As the insulating layer (11), there can be used glass, an epoxy prepregtogether with glass-epoxy prepreg, glass-polyimide prepreg, etc, thesematerials being formed by a press laminate method. Alternatively, theinsulating layer (11) can be formed by coating an epxoy resin varnish ora polyimide varnish.

Then, as shown in FIG. 5, organic materials are removed by exposing to alaser beam to form a hole (14) wherein a conductive hole (6) forconnecting the ground layer (1) to the conductive shield (5) of coaxialconductor (4) is to be formed, and to form a hole (14') wherein aconductive hole (8) for connecting the central signal conductor (7) ofcoaxial conductor (4) to other conductors is to be formed. In the caseof forming the hole (14'), the insulating layer (11), the adhesiveinsulating layer (3) and the circuit substrate (2') are exposed to thelaser beam to expose the conductive shield (5) (step C). In such a case,the laser beam is irradiated from the two directions, that is, from theinsulating layer (11) side and from the circuit substrate (2') side inorder to expose the conductive shield (5) completely.

As the laser beam, it is preferable to use CO₂ laser in order to easilyremove the organic materials of the insulating layer (11) and theadhesive insulating layer (3) and to hardly remove the metallic layer ofthe conductive shield (5). It is also possible to use YAG laser, excimerlaser, or the like, singly or in combination with CO₂ laser.

Then, as shown in FIG. 6, a metal plated layer such as a copper layer isformed on the hole (14) by an electroless metal plating or a combinationof an electroless metal plating and electric metal plating (step D).Then, the conductive hole (6) is formed by a conventional method. On theother hand, the conductive shield (5) of the coaxial conductor on theportion of forming the conductive hole (8) is removed by etching (stepE).

In the next place, as shown in FIG. 7, at least one substrate thusobtained and at least one inner layer plate (12) are laminated via aprepreg (11') and pressed under pressure with heating to obtain anintegral structure, while the hole (14') from which the insulatingmaterial is removed is filled with a resin (step F). Then, a hole isdrilled and an inner wall of the drilled hole is metallized by plating,followed by formation of the conductive hole (8) and a surface patternby a conventional method (step G).

As the resin for filling the hole (14'), there can be used an epoxyresin, a phenolic resin, a polyimide resin, or the like.

The formation of the conductive hole (6), the conductive hole (8) andthe surface pattern can be carried out by a conventional method asmentioned above. It is also possible to use an additive method.

The thus obtained wiring board does not bring about the crosstalk noisedue to the use of coaxial conductors with the special connection method,and can attain high speed transmission of signal by using a materialhaving a low dielectric constant such as polytetrafluoroethylene (TFE),tetrafluoroethylene-hexafluoropropylene copolymer (FEP),ethylene-tetrafluoroethylene copolymer (ETFE),tetrafluoroethylene-perfluoroalkyl vinylether copolymer (PFA), etc. asthe conductor insulating layer (9) of coaxial conductor. Further, sincethe coaxial conductor is used, variation of property impedance are verysmall.

Further, since the method of removing the conductive shield and theconductive insulating layer together with the insulating material by thelaser beam as taught by the first method disclosed in U.S. Pat. No.4,743,710 is not employed in the present invention, the shielding effectis improved by (a) reflecting the laser beam by the conductive shield(5), retaining the conductive shield (5) and inner materials of coaxialconductor, and obtaining selective connection between the conductiveshield (5) and the circuit substrate (2') by the conductive hole (6),and (b) selectively removing a part of the conductive shield (5) at theportion to be connected with other circuits of the circuit substrate(2') while not connecting with the ground layer (1), filling with theresin in the hole (14'), drilling a hole so as not to contact with theconductive shield (5) a part of which has been removed, metallizing theinner wall of the drilled hole to form the conductive hole (8) toconnect to the central signal conductor (7), resulting in attainingselective connection of the conductive shield (5) and the central signalconductor (7) of the coaxial conductor.

Further, by exposing both sides of the laminate to laser beam in theformation of the hole (14), the conductive shield (5) of coaxialconductor on the portion wherein the central signal conductor (7) is tobe connected is completely exposed, resulting in protecting the innerportion of the coaxial conductor under the conductive shield (5) withoutdamage. For such a purpose, it is not preferable to use the organicelectroconductive substances as disclosed in U.S. Pat. No. 4,743,710 asthe conductive shield (5). In the present invention, knitted wire,copper foil or copper plated metal layer is used as the conductiveshield (5).

On the other hand, the connection metal layer built-in type wiring boardhas a structure as shown in FIG. 2 comprising a ground layer (1), aninsulating substrate (2) formed thereon, an adhesive insulating layer(3) formed n the insulating substrate (2), at least one coaxialconductor (4) with a desired shape fixed on the surface of the adhesiveinsulating layer (3), an insulating layer (11) covering the coaxialconductor (4), and at least one conductive hole (8) an inner wall ofwhich is covered with a metal film connected to a central signalconductor (7) of coaxial conductor (4), the conductive shield (5) ofcoaxial conductor being connected to the ground layer (1) by connectionmetal layers (6'), the inner wall metallized conductive hole (8) beingconnected to the central signal conductor (7) of coaxial conductor usingthe coaxial conductor (4) from which a part of the conductive shield (5)has been selectively removed. As a result, the connecting portion canform a coaxial conductor structure by making the metallized hole (8) acentral signal conductor, the insulating resin (11) surrounding the hole(8), and the connection metal layer (6') surrounding a part of theinsulating resin.

Such a wiring board can be produced by process as shown in FIGS. 3, 4and 9-17.

One process comprises:

(A) fixing a plurality of coaxial conductors (4) with a desired shape onthe adhesive insulating layer (3) formed on the insulating substrate (2)(shown in FIG. 3),

(B) forming the insulating layer (11), on the coaxial conductors (4)(not shown in a drawing),

(C) exposing parts of the insulating layer (11), the adhesive insulatinglayer (3) and the insulating substrate (2) to laser beam so as to removeunnecessary portions for forming the connection metal layers (6') (shownin FIG. 4),

(D) removing only a part of the conductive shield (5) retained by laserbeam removal in the step (C) by etching (not shown in a drawing),

(E) forming the connection metal layers (6') by plating on exposedconductor insulating layer (9) in the case when an adhesive layer havingplating metal depositing properties is formed on the surface of theconductor insulating layer (9) (the surface of fluorine resin orpolyimide being generally smooth and not plated) and exposed insulatinglayer (11) and adhesive insulating layer (3), and the whole surfaces ofthe insulating substrate (2) and the insulating layer (11) to form theground layers (1), and for connecting at least two ground layers (1) andfor connecting the conductive shield (5) of coaxial conductor to theground layer (1) (shown in FIG. 9),

(F) filling the portion removed by the laser beam with an insulatingresin (21) (shown in FIG. 10),

(G) drilling a hole at the portion filled with the insulating resin (21)so as to expose terminals of the central signal conductor (7) and theconductor insulating layer (9) of coaxial conductor or cross-sectionthereof and so as to be insulated from the conductive shield (5) ofcoaxial conductor and the connection metal layers (6') and the groundlayer (1) formed in the step (E) (shown in FIG. 11), and

(H) metallizing the inner wall of the hole drilled in the step (G) toobtain the wiring board shown in FIG. 2.

Another process for producing the wiring board of FIG. 2 comprises;

(A) fixing a plurality of coaxial conductors (4) with a desired shape onthe adhesive insulating layer (3) formed on the insulating substrate (2)(shown in FIG. 3),

(B) forming the insulating layer (11) on the coaxial conductors (4) (notshown in a drawing),

(C) exposing parts of the insulating layer (11), the adhesive insulatinglayer (3) and the insulating substrate (2) to laser beam so as to removeunnecessary portions for forming the connection metal layers (6') (shownin FIG. 4),

(D) forming the connection metal layers (6') by plating on exposedconductive shield (5), exposed insulating layer (11) and adhesiveinsulating layer (3), and the whole surfaces of the insulating substrate(2) and the insulating layer (11) to form the ground layers (1), and forconnecting at least two ground layers (1) and for connecting theconductive shield (5) of coaxial conductor to the ground layer (1)(shown in FIG. 12),

(E) filling the portion removed by the laser beam in the step (D) withan insulating resin (21) (shown in FIG. 13),

(F) removing a part of the insulating resin (21) by exposing to laserbeam in a range narrower than the connecting portions of the connectionmetal layers (6') while exposing the terminal of the coaxial conductor(4) including the central signal conductor (7), the conductor insulatinglayer (9) and the conductive shield (5) and the ground layers formedaround the coaxial conductor (4) to the resulting hole (shown in FIG.14),

(G) removing the conductive shield (5) of coaxial conductor exposed tothe hole by etching (not shown in a drawing),

(H) filling the portion removed by the laser beam in the step (F) withan insulating resin (22) (shown in FIG. 15),

(I) drilling a hole (8) at the portion filled with the insulating resin(22) so as to expose terminals of the central signal conductor (7) andthe conductive insulating layer (9) of coaxial conductor orcross-section thereof and so as to be insulated from the conductiveshield (5) of coaxial conductor, and the ground layer (1) and theconnection metal layers (6') formed in the step (F) (shown in FIG. 16),and

(J) metallizing the inner wall of the hole drilled in the step (I)(shown in FIG. 17).

As the insulating substrate (2), there can be used commerciallyavailable ones such as an epoxy resin substrate, a phenol resinsubstrate, a fluorine resin substrate; cloth or paper using inorganicfibers such as glass cloth, glass paper, etc; cloth or paper usingorganic fibers such as cellulose, aramide, nylon fibers, polyesterfibers, etc., impregnated with an epoxy resin, a phenol resin, etc. orcoated with a dispersion of a fluorine resin, followed by baking; theabove-mentioned resins mixed with an inorganic filler such as glassshort fibers; organic polymer films such as a polyimide film, apolyester film, a polyethylene film, a polypropylene film, apolyamideimide film, a polyether ketone film, a polyetherimide film, afluorine-containing polymer film such as polytetrafluoroethylene film,etc. It is also possible to use photocurable resins, and the resinsmentioned above mixed with a catalyst for electroless plating.

As the adhesive insulating layer (3), the coaxial conductor (4), theconductor adhesive layer (13), the central signal conductor (7), theconductor insulating layer (9), and the insulating layer (11), there canbe used the same materials as used in the production of the inner wallmetallized conductive hole containing type wiring board.

As the laser beam, the same ones mentioned above can also be used.

As the insulating resins (21) and (22) for filling the hole removed bythe laser beam, there can be used an epoxy resin, a phenol resin, apolyimide resin, etc. Preferable resins are those having the sameproperties as the insulating substrate (2).

The thus produced wiring board is excellent in preventing the crosstalknoise due to the use of the coaxial conductors with the specialconnection method. Further, since distances of connecting portionbetween the central signal conductor (7) and other circuits, andconnecting portion between the conductive shield (7) and the groundlayer (1) can be made small, influences on signals due to deviation ofthe designed impedance can be minimized.

Further, in the connection metal layer built-in type wiring board, sincethe connection metal layers (6') take a structure corresponding to theconductive shield (5) of coaxial conductor and the metallized inner wallof the conductive hole (8) take a structure corresponding to the centralsignal conductor (7) of coaxial conductor, the effects of using thecoaxial conductor are further enhanced.

The present invention is illustrated by way of the following Examples,in which all parts and percents are by weight, unless otherwisespecified.

In the following Examples, the following resin compositions were used.

COMPOSITION I

A composition was prepared by mixing 300 g of the following resins witha solution of 50 g of N-methyl-2-pyrrolidone dissolving 1 g of palladiumchloride.

    ______________________________________                                        Ethylene glycol monoethyl ether acetate                                                                600    g/l                                           (ethyl Cellosolve acetate; mfd. by                                            Tokyo Kasei Kogyo Co., Ltd.)                                                  Epoxy resin (Epikote 1001, mfd.                                                                        109    g/l                                           by Yuka Shell Epoxy Co., Ltd.)                                                Acrylonitrile-butadiene copolymer                                             rubber (Nitrile Rubber Nipol DN 401,                                                                   20     g/l                                           mfd. by Nippon Zeon Co., Ltd.)                                                Phenol resin (Hitanol 2400, mfd.                                                                       60     g/l                                           by Hitachi Chemical Co., Ltd.)                                                Acrylonitrile-butadiene copolymer                                             (Nipol 1432J, mfd. by Nippon                                                                           144    g/l                                           Zeon Co., Ltd.)                                                               Silicon dioxide powder (Crystalite                                                                     50     g/l                                           VX-X, mfd. by Tatsumori K.K.)                                                 [Composition II]                                                              Phenoxy resin (phenotohto YP-50,                                                                       100    parts                                         mfd. by Tohto Kasei Co., Ltd.)                                                Methylated melamine (Melan 523,                                                                        15     parts                                         mfd. by Hitachi Chemical Co., Ltd.)                                           Glass short fibers (AGP-01BZ, mfd.                                                                     35     parts                                         by Asahi-Schwebel Co., Ltd.)                                                  m-Bromobenzoic acid (mfd. by Wako                                                                      0.3    part                                          Pure Chemical Industries, Ltd.)                                               Palladium catalyst for electroless                                            plating (Cat. #11, mfd. by Hitachi                                                                     2.5    part                                          Chemical Co., Ltd.)                                                           Ethyl Cellosolve acetate (mfd. by                                                                      220    parts                                         Tokyo Kasei Kogyo Co., Ltd.)                                                  [Composition III]                                                             Phenoxy resin (Phenotohto YP-50,                                                                       70     parts                                         mfd. by Tohto Kasei Co., Ltd.)                                                Epoxy resin (Epikote 828, mfd. by                                                                      20     parts                                         Yuka Shell Epoxy Co., Ltd.)                                                   Epoxy resin (DEN 438, mfd. by Dow                                                                      10     parts                                         Chemical Co.)                                                                 Polyvinyl butyral resin (Eslex BM-2,                                                                   20     parts                                         mfd. by Sekisui Chemical Co., Ltd.)                                           Methylated melamine (Melan 523,                                                                        20     parts                                         mfd. by Hitachi Chemical Co., Ltd.)                                           Imidazole derivative (2PZ-CNS, mfd.                                                                    2      parts                                         by Shikoku Kasei Co., Ltd.)                                                   Silicon dioxide powder (Crystalite VX-X,                                                               20     parts                                         mfd. by Tatsumori K.K.)                                                       Ethyl Cellosolve acetate (mfd. by                                                                      200    parts                                         Tokyo Kasei Kogyo Co., Ltd.)                                                  ______________________________________                                    

EXAMPLE 1

An etching resist was formed on desired portions of both surfaces ofdouble-sided roughened copper-clad glass polyimide laminate (MCL-1-67, atrade name, mfd. by Hitachi Chemical Co., Ltd.) and unnecessary copperfoil on the portions to be formed into conductive holes (6) and (8) wasremoved by etching to prepare a circuit substrate (2') having a groundlayer (1) (see FIG. 1). A dry film of 100 μm thick was prepared fromComposition I and laminated on a surface of the circuit substrate (2')under press conditions of 150° C., and 10 kg/cm² for 10 minutes. Coaxialconductors having an outer diameter of 0.22 mm, a diameter of thecentral signal conductor of 0.075 mm, the thickness of the conductiveshield of 0.01 mm, and the conductor insulating layer made from fluorineresin were wired in the desired pattern according to a wiring rule so asto make the wiring density 2 wires/2.54 mm and the wire pitch 0.45 mmusing a numerical controlling wiring machine.

Then, a dry film of 180 μm thick made from Composition II was laminatedon the coaxial conductor positioned surface and pressed at 150° C. and10 kg/cm² for 10 minutes, followed by pressing with heating at 170° C.and 30 kg/cm² for 90 minutes to obtain an integrated structure.

Focussed CO₂ laser beam having a spot diameter of 200 μm was irradiatedwith an output of 45 W on a portion of the resulting substrate to beformed into a conductive hole (6). The hole (6) was to be plated in alater step so as to be connected to the ground layer. The size of thehole (6) should be sufficiently large for the connection and for fullycontacting with a plating solution, and usually 0.5 to 1.0 mm indiameter. Such a hole was formed by irradiating the laser beam whilescanning. In this Example, the hole diameter was 0.5 mm. Further,focussed CO₂ laser beam having a spot diameter 200 μm was irradiated ona portion of the resulting substrate to be formed into a conductive hole(8). The hole (8) was formed so as to remove the conductive shield (5)of coaxial conductor in a later step. Thus, the hole (8) should beformed so as not to contact with a hole formed in a later step forconnecting to the central signal conductor (7), even if working errortakes place. In this Example, the hole (8) was formed in the same manneras forming the hole (6) so as to make the diameter 1.7 mm using thelaser beam while scanning.

The resulting substrate was washed, provided with a catalyst forelectroless plating, accelerated in adhesion, and dipped in anelectroless copper plating solution (Hid-410, a trade name, mfd. byHitachi Chemical Co., Ltd.) for 10 hours to form a copper plated layerof 25 μm thick. Then, an etching resist was formed only on the portionto be formed into a conductive hole (6) to remove unnecessary copperplated layer by etching.

The resulting substrate, an inner layer made by an etched foil method, aglass-polyimide prepreg (GIA-67N, a trade name mfd. by Hitachi ChemicalCo., Ltd.) and a copper foil were piled and pressed at 180° C. and 30kg/cm² for 90 minutes to obtain an integrated structure. As a result,the hole (8) was filled with the polyimide resin contained in theglass-polyimide prepreg. On desired portions of the resulting substrate,holes of 0.8 mm in diameter were drilled, washed, provided with acatalyst for electroless plating, accelerated in adhesion and subjectedto electroless copper plating to form electroless copper plated layersof about 35 μm on the inner wall of the hole and the surface of copperfoil. Etching resists were formed on necessary portions such as pads andterminals for mounting electronic parts to remove unnecessary copper byetching. As a result, a wiring board as shown in FIG. 1 was obtained.

EXAMPLE 2

On a double-sided roughened copper foil, Composition III was coated toform a film of 100 μm thick, followed by heating at 120° C. for 30minutes, and 160° C. for 30 minutes. Then, an etching resist was formedon the resulting film, followed by removal of copper foils from theportions to be formed into conductive holes (6) and (8) to prepare acircuit substrate having a ground layer thereon.

A dry film of 100 μm thick was formed from Composition I, and laminatedon the copper foil surface of the circuit substrate under pressconditions of 150° C. and 10 kg/cm² for 10 minutes. The same coaxialconductors as used in Example 1 except for covered with epoxyresin/nylon adhesive layer of 10 μm thick were wired in the desiredpattern according to a wiring rule so as to make the wiring density 2wires/2.54 mm and the wire pitch 0.45 mm using a numerical valuecontrolling wiring machine.

Then, using the same procedure as used in Example 1 a wiring board asshown in FIG. 1 was produced.

EXAMPLE 3

A circuit substrate having a ground layer was prepared by impregratingaramide fibers with Composition III, half-curing the impregnated aramidefibers, laying surface roughened double-sided copper foils of 35 μmthick on a side thereof, pressing at 160° C. and 30 kg/cm² for 60minutes to obtain an integrated structure, forming etching resists onsurfaces of the resulting substrate and removing copper foils on theportions to be formed into conductive holes (6) and (8) by etching.

Then, using the same procedure as used in Example 1, a wiring board asshown in FIG. 1 was produced.

EXAMPLE 4

The process of Example 1 was repeated except for using coaxialconductors having an outer diameter of 0.18 mm, a central signalconductor with a diameter of 0.06 mm, a conductive shield of 0.01 mmthick, and a conductor insulating layer made from a polyimide resin.

The wiring boards produced in Examples 1 to 4 showed no crosstalk noisewhen measured under the following conditions:

    ______________________________________                                        Distance between conductors:                                                                          0.4    mm                                             Length of conductors positioned in                                                                    30     cm                                             parallel:                                                                     Induction pulse potential:                                                                            5      V                                              Induction pulse width:  500    ns                                             Induction pulse rise time:                                                                            1      ns                                             ______________________________________                                    

On the other hand, when signal conductors having conductor insulatinglayers but having no conductive shield were used, the resulting wiringboard showed the crosstalk noise of 4 to 4.5%.

This shows great effects of the wiring boards of the present invention.

EXAMPLE 5

A glass-polyimide insulating plate of 0.2 mm thick and cured completelywas prepared.

A dry film of 100 μm thick was made from Composition I and laminated ona surface of the substrate by pressing at 150° C. and 10 kg/cm² for 10minutes. Then, coaxial conductors having an outer diameter of 0.22 mm, adiameter of the central signal conductor of 0.075 mm, the thickness ofthe conductive shield of 0.01 mm, and the conductor insulating layermade from a fluorine resin (the surface of the conductor insulatinglayer (9) being smooth, and thus not plated) were wired in the desiredpattern according to a wiring rule so as to make the wiring density 2wires/2.54 mm and the wire pitch 0.4 mm using a numerical valuecontrolling wiring machine.

Then, a dry film of 180 μm thick made from Composition II was laminatedon the coaxial conductor positioned surface and pressed at 150° C. and10 kg/cm² for 10 minutes, followed by pressing with heating at 170° C.and 30 kg/cm² for 90 minutes to obtain an integrated structure.

Focussed CO₂ laser beam having a spot diameter of 200 μm was irradiatedwith an output of 45 W on a portion of the resulting substrate to beformed into a connection metal layer to remove the resin so as to make ahole diameter 2 mm and so as to expose the conductive shield of coaxialconductor when viewed from both sides of the substrate. Then, theexposed conductive shield was removed by etching using a cupric chloridesolution.

The resulting substrate was washed, provided with a catalyst forelectroless plating, accelerated in adhesion, and dipped in anelectroless copper plating solution (Hid-410, a trade name, mfd. byHitachi Chemical Co., Ltd.) for 10 hours to form a copper plated layerof 25 μm thick. No copper plating was deposited on the conductorinsulating layer of coaxial conductor at this time.

The resulting substrate, an inner plate prepared by an etched foilmethod, a glass-polyimide-made prepreg (GIA-67N, a trade name, mfd. byHitachi Chemical Co., Ltd.) and a copper foil were laminated and pressedat 180° C. and 30 kg/cm² for 90 minutes to obtain an integratedstructure. As a result, the hole was filled with the polyimide resincontained in the glass-polyimide prepreg. Then, desired portions of theresulting substrate and the portions from which the condutive shield hadbeen removed and not contacted with the above-mentioned conductiveshield were drilled to form holes of 0.8 mm in diameter, followed bywashing, providing with a catalyst for electroless plating, acceleratingin adhesion and conducting electroless copper plating to form copperplated layers of about 35 μm thick on inner wall of the hole and thesurface of copper foil. Etching resists were formed on necessaryportions such as pads and terminals for mounting electronic parts toremove unnecessary copper by etching to produce a wiring board as shownin FIG. 2.

EXAMPLE 6

A glass-polyimide insulating plate of 0.2 mm thick and cured completelywas prepared.

A dry film of 100 μm thick was made from Composition I and laminated ona surface of the circuit substrate by pressing at 150° C. and 10 kg/cm²for 10 minutes. Then, coaxial conductors having an outer diameter of0.22 mm, a diameter of the central signal conductor of 0.075 mm, thethickness of the conductive shield of 0.01 mm, the conductor insulatinglayer made from a fluorine resin, the conductor insulating layer beingcovered with as adhesive resin an epoxy resin layer mixed with aluminumsilicate adsorbing palladium which is a catalyst for plating, the epoxyresin layer being covered with a copper film obtained by electrolessplating as a conductive shield, were wired in the desired patternaccording to a wiring rule so as to make the wiring density 2 wires/2.54mm and the wire pitch 0.4 mm using a numerical value controlling wiringmachine.

Then, a dry film of 180 μm thick made from Composition II was laminatedon the coaxial conductor positioned surface and pressed at 150° C. and10 kg/cm² for 10 minutes, followed by pressing with heating at 170° C.and 30 kg/cm² for 90 minutes to obtain an integrated structure.

Focused CO₂ laser beam having a spot diameter of 200 μm irradiated withan output of 45 W on a portion of the resulting substrate to be formedinto a connection metal layer to remove the resin so as to make a holediameter 4 mm and so as to expose the conductive shield of coaxialconductor when viewed from both sides of the substrate.

The resulting substrate was washed, provided with a catalyst forelectroless plating, accelerated in adhesion, and dipped in anelectroless copper plating solution (Hid-410, a trade name, mfd. byHitachi Chemical Co., Ltd.) for 10 hours to form a copper plated layerof 25 μm thick.

Then, Composition III was coated on surfaces of the substrate and theportion removed by the laser, followed by curing of the resin bysandwiching with a pair of stainless steel plates at 170° C. and 30kg/cm² for 90 minutes.

Further, the portion to be formed into a connection metal layer wasexposed to CO₂ laser of which spot diameter was focussed to 200 μm withan output of 45 W to remove the resin so as to make the hole diameter 2mm, resulting in exposing the conductive shield of coaxial conductor sothat the exposed conductive shield was able to be seen from the bothsides of the substrate.

Then, the exposed conductive shield was removed by etching using anaqueous solution of cupric chloride.

In the next place, Composition III was coated on surfaces of thesubstrate and the portion removed by the laser, followed by curing ofthe resin by sand-wiching with a pair of stainless steel plates at 170°C. and 30 kg/cm² for 90 minutes.

The resulting substrate, an inner plate prepared by an etched foilmethod, a glass-polyimide-made prepreg (GlA-67N, a trade name, mfd. byHitachi Chemical Co., Ltd.) and a copper foil were laminated and pressedat 180° C. and 30 kg/cm² for 90 minutes to obtain an integratedstructure. Then, desired portions of the resulting substrate and theportions from which the conductive shield had been removed and notcontacted with the above-mentioned conductive shield were drilled toform holes of 0.8 mm in diameter, followed by washing, providing with acatalyst for electroless plating, accelerating in adhesion, andconducting electroless copper plating to form copper plated layers ofabout 35 μm thick on inner wall of the hole and the surface of copperfoil. Etching resists were formed on necessary portions such as pads andterminals for mounting electronic parts to remove unnecessary copper byetching to produce a wiring board (not shown in a drawing).

The wiring boards produced in Examples 5 and 6 showed no crosstalk noisewhen measured under the following conditions:

    ______________________________________                                        Distance between conductors:                                                                          0.4    mm                                             Length of conductors positioned                                                                       30     cm                                             in parallel:                                                                  Induction pulse potential:                                                                            5      V                                              Induction pulse width:  500    ns                                             Induction pulse rise time:                                                                            1      ns                                             ______________________________________                                    

On the other hand, when a land on the surface of wiring board connectedto the central signal conductor of coaxial conductor, and a land formedon very near place thereof and connected to the ground layer wereterminated with a resistance of 50 ohms, distance of wave form byreflection was not generated nor observed.

As explained above, the wiring board excellent in controlling thecrosstalk noise and controlling the interference by reflection can easybe obtained and effectively be produced according to the presentinvention.

What is claimed is:
 1. A coaxial interconnection wiring boardcomprising:a ground layer, an insulating substrate formed on the groundlayer, an adhesive insulating layer formed on the insulating substrate,at least one coaxial conductor with a conductive shield fixed on asurface of the adhesive insulating layer, an insulating layer coveringthe coaxial conductor, at least one conductive hole having an inner wallcovered with a metal film connected to a central signal conductor of thecoaxial conductor, the conductive shield of the coaxial conductorconnected to the ground layer by connection metal layers, the inner wallof the metallized conductive hole connected to the central signalconductor using the coaxial conductor from which a portion of theconductive shield has been selectively removed, and an additionalconductor insulating layer including an insulating resin surrounding themetallized conductor hole, wherein the connection metal layers surrounda part of the additional conductor insulating layer.
 2. A coaxialinterconnection wiring board, according to claim 1, further comprisingan additional coaxial conductor including the conductive hole, theadditional conductor insulating layer, and the connection metal layers.